Given the significant costs and chronic disability associated with falls, more emphasis must be given to and controlling factors responsible for falls in high risk industries. Localized muscle fatigue is an important risk factor for slips and falls in the high risk construction and manufacturing industries, because the most common activities performed prior to falls from elevations are static postural activities and manual materials handling. The purpose of this study will be to evaluate the effect of localized fatigue on standing steadiness. The study's broad long-term objective will be to suggest practical ergonomic guidelines for the evaluation and control of static work activities and manual lifting, based on their potential impact on human postural stability. Experiment I (Yr. I) will determine the effects of localized fatigue on standing steadiness and compensatory adjustments to maintain balance. The experiment will determine which relevant postural muscle groups, when subjected to isometric muscle fatigue, cause significant changes in the subjects' standing postural stability. This mechanistic information will provide a conceptual framework for explaining the effects on postural stability of more complex static work postures and manual lifting tasks. Experiment 11 (Yr. I) will determine the effect of performing static work in the stooped vs partial squat vs erect posture for different time periods on standing postural stability. Fatigue estimates of endurance time, heart rate and Borg's Rating of Perceived Exertion (RPE) will provide information needed to develop appropriate rest periods for static work with the stooped versus partial squat vs erect posture for three different postural combinations of the postural muscles tested in Experiment I. Experiment III (Yr. II) will then determine whether manual lifting from the stooped vs partial squat vs erect posture results in a significant impairment of postural stability at low and moderate lifting frequencies. The localized fatigue component of repetitive manual lifting will be estimated by the parameters of postural stability, heart rate and Borg's RPE.